Reducing peak current usage in light emitting diode array

ABSTRACT

Embodiments relate to driving first light emitting diodes (LEDs) of a first color to emit light during first subframes of emission frames, driving second LEDs of a second color to emit light during second subframes of emission frames, and driving third LEDs of a third color to emit light during the second subframes of emission frames. Light emitted from the first, second, and third LEDs is directed onto a mirror that reflects the light onto a plurality of pixel locations of an image field. The first, second, and third LEDs are aligned on an array of LEDs such that the first LEDs are at a first distance away from the second LEDs, and the first LEDs are at a second distance away from the third LEDs.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Greek Patent Application No.20190100204, filed May 9, 2019, which is incorporated by reference inits entirety.

BACKGROUND

This disclosure relates to a display device, and specifically to adisplay device with at least a subset of light emitting diodes (LEDs)turned on at different times to reduce peak current.

A display device is often used in a virtual reality (VR) oraugmented-reality (AR) system as a head-mounted display or a near-eyedisplay. The display device typically includes an array of LEDs thatemits light to the eyes of the viewer, and an optical block positionedbetween the display and the eyes. The optical block includes opticalcomponents that receive light emitted from the array and adjust anorientation of the light such that the light is projected onto an imagefield to form an image. To display an image via the display device, thearray of LEDs emits light, and the light is projected onto pixellocations on the image field.

In a given display device, the array of LEDs may include a large numberof LEDs (e.g., 2560 LEDs) for each of the colors used to display animage (e.g., Red, Blue, Green) and turning on all of the LEDs (e.g.,7,680 LEDs) in the array simultaneously consumes a large amount ofinstantaneous current. When a large amount of current is required todrive the array of LEDs, a complicated system design of the displaydevice may be needed to supply the driving current to the array of LEDs.However, developing and manufacturing a complicated system design is atime intensive and costly process. Further, when a large amount ofcurrent is used to operate the display device, there is a risk ofdegraded silicon performance, which can lead to increase in defectiveproducts and shorter lifetime of the display device.

SUMMARY

Embodiments relate to projecting light from an array of LEDs onto animage field to display an image to a user. Light emitted from the arrayof LEDs may be directed to a rotating mirror and redirected to the imagefield by the rotating mirror that is positioned in between the array ofLEDs and the image field. Depending on the orientation of the mirror,light is directed to illuminate a particular subset of pixel locationson the image field. As the mirror rotates, light is projected ontodifferent subsets of the pixel locations, and an image is generated onthe image field when the mirror scans through the entire image field.The array of LEDs may include a plurality of LEDs (e.g., 2560 LEDs) foreach color (e.g., red, blue, green) that are arranged such that LEDs ofa same color are in a same row. When driving the array of LEDs to emitlight, different subsets of LEDs are turned on at different subframes ofan emission frame to reduce current usage at a given time.

In some embodiments, each emission frame for operating the array of LEDsis divided into two subframes. During a first subframe, first LEDs areturned on to emit light of a first color (e.g., red) while second LEDsof a second color (e.g., green) and third LEDs of a third color (e.g.,blue) are turned off. During a second subframe following the firstsubframe, the first LEDs are turned off while the second LEDs and thethird LEDs are turned on. The row of first LEDs is at a first distanceaway from the row of second LEDs, and the row of third LEDs is at asecond distance away from the row of second LEDs, where the firstdistance and the second distance are different. The first distance andthe second distance are determined based at least on emission timing offirst subframe and the second subframe such that light emitted from thefirst LEDs, second LEDs, and third LEDs are projected onto theappropriate pixel locations.

In some embodiments, each emission frame is divided into threesubframes. During a first subframe, first LEDs are turned on whilesecond LEDs and third LEDs are turned off. During a second subframe,second LEDs are turned on while first LEDs and third LEDs are turnedoff. During a third subframe, third LEDs are turned on while first LEDsand second LEDs are turned off. The row of first LEDs is at a firstdistance away from the row of second LEDs, and the row of third LEDs isat a second distance away from the row of second LEDs, where the firstdistance and the second distance are equal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a near-eye-display (NED), in accordancewith an embodiment.

FIG. 2 is a cross-sectional diagram of an eyewear of the NED illustratedin FIG. 1, in accordance with an embodiment.

FIG. 3A is a perspective view of a display device, in accordance with anembodiment.

FIG. 3B illustrates a block diagram of a source assembly, in accordancewith an embodiment.

FIG. 4 is a diagram illustrating an array of light emitting diodes(LEDs), in accordance with an embodiment.

FIG. 5A is a diagram illustrating projection of light emitted from LEDsonto an image field, in accordance with an embodiment.

FIG. 5B is a diagram illustrating rows of pixel locations on an imagefield, in accordance with an embodiment.

FIG. 6A is a timing diagram illustrating emission patterns of LEDs withtwo subframes in a single frame, in accordance with an embodiment.

FIG. 6B is a timing diagram illustrating emission patterns of LEDs withthree subframes in a single frame, in accordance with an embodiment.

FIGS. 7A-7C are conceptual diagrams illustrating rows onto which LEDsproject light for emission frames with two subframes, in accordance withan embodiment.

FIGS. 8A-8C are conceptual diagrams illustrating rows onto which LEDsproject light for emission frames with three subframes, in accordancewith an embodiment.

FIG. 9 is flowchart depicting a process of operating a display device,in accordance with an embodiment.

The figures depict embodiments of the present disclosure for purposes ofillustration only.

DETAILED DESCRIPTION

Embodiments relate to operating a display device to reduce peak currentusage by an array of LEDs of the display device used to display images.Instead of turning on all of the LEDs on the array at the same time whendisplaying an image, first LEDs of a first color are driven to emitlight during first subframes of emission frames while second LEDs of asecond color are disabled. During second subframes of the same emissionframes, second LEDs are driven to emit light while first LEDs aredisabled.

Embodiments of the invention may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

Near-Eye Display

FIG. 1 is a diagram of a near-eye display (NED) 100, in accordance withan embodiment. The NED 100 presents media to a user. Examples of mediapresented by the NED 100 include one or more images, video, audio, orsome combination thereof. In some embodiments, audio is presented via anexternal device (e.g., speakers and/or headphones) that receives audioinformation from the NED 100, a console (not shown), or both, andpresents audio data based on the audio information. The NED 100 mayoperate as a VR NED. However, in some embodiments, the NED 100 may bemodified to also operate as an augmented reality (AR) NED, a mixedreality (MR) NED, or some combination thereof. For example, in someembodiments, the NED 100 may augment views of a physical, real-worldenvironment with computer-generated elements (e.g., images, video,sound, etc.).

The NED 100 shown in FIG. 1 includes a frame 105 and a display 110. Theframe 105 includes one or more optical elements which together displaymedia to users. The display 110 is configured for users to see thecontent presented by the NED 100. As discussed below in conjunction withFIG. 2, the display 110 includes at least a source assembly to generatean image light to present media to an eye of the user. The sourceassembly includes, e.g., a light source, an optics system, or somecombination thereof.

FIG. 1 is only an example of a VR system. However, in alternateembodiments, FIG. 1 may also be referred to as a Head-Mounted-Display(HMD).

FIG. 2 is a cross sectional diagram 200 of the NED 100 illustrated inFIG. 1, in accordance with an embodiment. The cross section 200illustrates at least one waveguide assembly 210. An exit pupil is alocation where the eye 220 is positioned in an eyebox region 230 whenthe user wears the NED 100. In some embodiments, the frame 105 mayrepresent a frame of eye-wear glasses. For purposes of illustration,FIG. 2 shows the cross section 200 associated with a single eye 220 anda single waveguide assembly 210, but in alternative embodiments notshown, another waveguide assembly which is separate from the waveguideassembly 210 shown in FIG. 2, provides image light to another eye 220 ofthe user.

The waveguide assembly 210, as illustrated below in FIG. 2, directs theimage light to the eye 220 through the exit pupil. The waveguideassembly 210 may be composed of one or more materials (e.g., plastic,glass, etc.) with one or more refractive indices that effectivelyminimize the weight and widen a field of view (hereinafter abbreviatedas ‘FOV’) of the NED 100. In alternate configurations, the NED 100includes one or more optical elements between the waveguide assembly 210and the eye 220. The optical elements may act (e.g., correct aberrationsin image light emitted from the waveguide assembly 210) to magnify imagelight emitted from the waveguide assembly 210, some other opticaladjustment of image light emitted from the waveguide assembly 210, orsome combination thereof. The example for optical elements may includean aperture, a Fresnel lens, a convex lens, a concave lens, a filter, orany other suitable optical element that affects image light. In oneembodiment, the waveguide assembly 210 may produce and direct many pupilreplications to the eyebox region 230, in a manner that will bediscussed in further detail below in association with FIG. 5B.

FIG. 3A illustrates a perspective view of a display device 300, inaccordance with an embodiment. In some embodiments, the display device300 is a component (e.g., the waveguide assembly 210 or part of thewaveguide assembly 210) of the NED 100. In alternative embodiments, thedisplay device 300 is part of some other NEDs, or another system thatdirects display image light to a particular location. Depending onembodiments and implementations, the display device 300 may also bereferred to as a waveguide display and/or a scanning display. However,in other embodiments, the display device 300 does not include a scanningmirror. For example, the display device 300 can include matrices oflight emitters that project light on an image field through a waveguidebut without a scanning mirror. In another embodiment, the image emittedby the two-dimensional matrix of light emitters may be magnified by anoptical assembly (e.g., lens) before the light arrives a waveguide or ascreen.

For a particular embodiment that uses a waveguide and an optical system,the display device 300 may include a source assembly 310, an outputwaveguide 320, and a controller 330. The display device 300 may provideimages for both eyes or for a single eye. For purposes of illustration,FIG. 3A shows the display device 300 associated with a single eye 220.Another display device (not shown), separated (or partially separated)from the display device 300, provides image light to another eye of theuser. In a partially separated system, one or more components may beshared between display devices for each eye.

The source assembly 310 generates image light 355. The source assembly310 includes a light source 340 and an optics system 345. The lightsource 340 is an optical component that generates image light using aplurality of light emitters arranged in a matrix. Each light emitter mayemit monochromatic light. The light source 340 generates image lightincluding, but not restricted to, Red image light, Blue image light,Green image light, infra-red image light, etc. While RGB is oftendiscussed in this disclosure, embodiments described herein are notlimited to using red, blue and green as primary colors. Other colors arealso possible to be used as the primary colors of the display device.Also, a display device in accordance with an embodiment may use morethan three primary colors.

The optics system 345 performs a set of optical processes, including,but not restricted to, focusing, combining, conditioning, and scanningprocesses on the image light generated by the light source 340. In someembodiments, the optics system 345 includes a combining assembly, alight conditioning assembly, and a scanning mirror assembly, asdescribed below in detail in conjunction with FIG. 3B. The sourceassembly 310 generates and outputs an image light 355 to a couplingelement 350 of the output waveguide 320.

The output waveguide 320 is an optical waveguide that outputs imagelight to an eye 220 of a user. The output waveguide 320 receives theimage light 355 at one or more coupling elements 350, and guides thereceived input image light to one or more decoupling elements 360. Thecoupling element 350 may be, e.g., a diffraction grating, a holographicgrating, some other element that couples the image light 355 into theoutput waveguide 320, or some combination thereof. For example, inembodiments where the coupling element 350 is diffraction grating, thepitch of the diffraction grating is chosen such that total internalreflection occurs, and the image light 355 propagates internally towardthe decoupling element 360. The pitch of the diffraction grating may bein the range of 300 nm to 600 nm.

The decoupling element 360 decouples the total internally reflectedimage light from the output waveguide 320. The decoupling element 360may be, e.g., a diffraction grating, a holographic grating, some otherelement that decouples image light out of the output waveguide 320, orsome combination thereof. For example, in embodiments where thedecoupling element 360 is a diffraction grating, the pitch of thediffraction grating is chosen to cause incident image light to exit theoutput waveguide 320. An orientation and position of the image lightexiting from the output waveguide 320 are controlled by changing anorientation and position of the image light 355 entering the couplingelement 350. The pitch of the diffraction grating may be in the range of300 nm to 600 nm.

The output waveguide 320 may be composed of one or more materials thatfacilitate total internal reflection of the image light 355. The outputwaveguide 320 may be composed of e.g., silicon, plastic, glass, orpolymers, or some combination thereof. The output waveguide 320 has arelatively small form factor. For example, the output waveguide 320 maybe approximately 50 mm wide along X-dimension, 30 mm long alongY-dimension and 0.5-1 mm thick along Z-dimension.

The controller 330 controls the image rendering operations of the sourceassembly 310. The controller 330 determines instructions for the sourceassembly 310 based at least on the one or more display instructions.Display instructions are instructions to render one or more images. Insome embodiments, display instructions may simply be an image file(e.g., bitmap). The display instructions may be received from, e.g., aconsole of a VR system (not shown here). Scanning instructions areinstructions used by the source assembly 310 to generate image light355. The scanning instructions may include, e.g., a type of a source ofimage light (e.g., monochromatic, polychromatic), a scanning rate, anorientation of a scanning apparatus, one or more illuminationparameters, or some combination thereof. The controller 330 includes acombination of hardware, software, and/or firmware not shown here so asnot to obscure other aspects of the disclosure.

FIG. 3B is a block diagram illustrating an example source assembly 310,in accordance with an embodiment. The source assembly 310 includes thelight source 340 that emits light that is processed optically by theoptics system 345 to generate image light 335 that will be projected onan image field (not shown). The light source 340 is driven by thedriving circuit 370 based on the data sent from a controller 330 or animage processing unit 375. In one embodiment, the driving circuit 370 isthe circuit panel that connects to and mechanically holds various lightemitters of the light source 340. The driving circuit 370 and the lightsource 340 combined may sometimes be referred to as a display panel 380or an LED panel (if some forms of LEDs are used as the light emitters).

The light source 340 may generate a spatially coherent or a partiallyspatially coherent image light. The light source 340 may includemultiple light emitters. The light emitters can be vertical cavitysurface emitting laser (VCSEL) devices, light emitting diodes (LEDs),microLEDs, tunable lasers, and/or some other light-emitting devices. Inone embodiment, the light source 340 includes a matrix of lightemitters. In another embodiment, the light source 340 includes multiplesets of light emitters with each set grouped by color and arranged in amatrix form. The light source 340 emits light in a visible band (e.g.,from about 390 nm to 700 nm). The light source 340 emits light inaccordance with one or more illumination parameters that are set by thecontroller 330 and potentially adjusted by image processing unit 375 anddriving circuit 370. An illumination parameter is an instruction used bythe light source 340 to generate light. An illumination parameter mayinclude, e.g., source wavelength, pulse rate, pulse amplitude, beam type(continuous or pulsed), other parameter(s) that affect the emittedlight, or some combination thereof. The light source 340 emits sourcelight 385. In some embodiments, the source light 385 includes multiplebeams of red light, green light, and blue light, or some combinationthereof.

The optics system 345 may include one or more optical components thatoptically adjust and potentially re-direct the light from the lightsource 340. One form of example adjustment of light may includeconditioning the light. Conditioning the light from the light source 340may include, e.g., expanding, collimating, correcting for one or moreoptical errors (e.g., field curvature, chromatic aberration, etc.), someother adjustment of the light, or some combination thereof. The opticalcomponents of the optics system 345 may include, e.g., lenses, mirrors,apertures, gratings, or some combination thereof. Light emitted from theoptics system 345 is referred to as an image light 355.

The optics system 345 may redirect image light 335 via its one or morereflective and/or refractive portions so that the image light 355 isprojected at a particular orientation toward the output waveguide 320(shown in FIG. 3A). Where the image light is redirected toward is basedon specific orientations of the one or more reflective and/or refractiveportions. In some embodiments, the optics system 345 includes a singlescanning mirror that scans in at least two dimensions. In otherembodiments, the optics system 345 may include a plurality of scanningmirrors that each scan in orthogonal directions to each other. Theoptics system 345 may perform a raster scan (horizontally, orvertically), a biresonant scan, or some combination thereof. In someembodiments, the optics system 345 may perform a controlled vibrationalong the horizontal and/or vertical directions with a specificfrequency of oscillation to scan along two dimensions and generate atwo-dimensional projected line image of the media presented to user'seyes. In other embodiments, the optics system 345 may also include alens that serves similar or same function as one or more scanningmirror.

In some embodiments, the optics system 345 includes a galvanometermirror. For example, the galvanometer mirror may represent anyelectromechanical instrument that indicates that it has sensed anelectric current by deflecting a beam of image light with one or moremirrors. The galvanometer mirror may scan in at least one orthogonaldimension to generate the image light 355. The image light 355 from thegalvanometer mirror represents a two-dimensional line image of the mediapresented to the user's eyes.

In some embodiments, the source assembly 310 does not include an opticssystem. The light emitted by the light source 340 is projected directlyto the waveguide 320 (shown in FIG. 3A).

The controller 330 controls the operations of light source 340 and, insome cases, the optics system 345. In some embodiments, the controller330 may be the graphics processing unit (GPU) of a display device. Inother embodiments, the controller 330 may be other kinds of processors.The operations performed by the controller 330 includes taking contentfor display, and dividing the content into discrete sections. Thecontroller 330 instructs the light source 340 to sequentially presentthe discrete sections using light emitters corresponding to a respectiverow in an image ultimately displayed to the user. The controller 330instructs the optics system 345 to perform different adjustment of thelight. For example, the controller 330 controls the optics system 345 toscan the presented discrete sections to different areas of a couplingelement of the output waveguide 320 (shown in FIG. 3A). Accordingly, atthe exit pupil of the output waveguide 320, each discrete portion ispresented in a different location. While each discrete section ispresented at different times, the presentation and scanning of thediscrete sections occur fast enough such that a user's eye integratesthe different sections into a single image or series of images. Thecontroller 330 may also provide scanning instructions to the lightsource 340 that include an address corresponding to an individual sourceelement of the light source 340 and/or an electrical bias applied to theindividual source element.

The image processing unit 375 may be a general-purpose processor and/orone or more application-specific circuits that are dedicated toperforming the features described herein. In one embodiment, ageneral-purpose processor may be coupled to a memory to execute softwareinstructions that cause the processor to perform certain processesdescribed herein. In another embodiment, the image processing unit 375may be one or more circuits that are dedicated to performing certainfeatures. While in FIG. 3B the image processing unit 375 is shown as astand-alone unit that is separate from the controller 330 and thedriving circuit 370, in other embodiments the image processing unit 375may be a sub-unit of the controller 330 or the driving circuit 370. Inother words, in those embodiments, the controller 330 or the drivingcircuit 370 performs various image processing procedures of the imageprocessing unit 375. The image processing unit 375 may also be referredto an as image processing circuit.

Light Emitting Diode Array

FIG. 4 is a top view of an array 400 of light emitting diodes (LEDs)that may be included in the light source 340 of FIGS. 3A and 3B, inaccordance with an embodiment. The array 400 includes a plurality ofLEDs that are organized into rows and columns. In the example shown inFIG. 4, the array 400 includes red LEDs 410, green LEDs 420, and blueLEDs 430 that are disposed such that LEDs of the same color are in thesame row. The green LEDs 420 are aligned along the red LEDs 410 on oneside of the green LEDs 420. The blue LEDs 430 are placed along a lineparallel to the red LEDs 410 and green LEDs 420 are placed on theopposite side of the green LEDs 420.

The row of red LEDs 410 is at a first distance D1 from the row of greenLEDs 420, and the row of blue LEDs 430 is at a second distance D2 fromthe row of green LEDs 420. The first distance D1 and the second distanceD2 is correlated with at least on a number of subframes of an emissionframe during display mode, as described in detail below with respect toFIGS. 6A and 6B. The first distance D1 and the second distance D2 may beequal or different from each other. Although not shown in FIG. 4,various other configurations of LEDs are also within the scope of thepresent disclosure. For example, the array 400 may include differentcolored LEDs, may have different color arrangements, and/or additionalrows of LEDs for each color.

While the LEDs shown in FIG. 4 are arranged in rows and columnsperpendicular to rows, in other embodiments, the LEDs on the array 400may be arranged in other forms. For example, some of the LEDs may bealigned diagonally or in other arrangement, regular or irregular,symmetrical or asymmetrical. Also, the terms rows and columns maydescribe two relative spatial relationships of elements. While, for thepurpose of simplicity, a column described herein is normally associatedwith a vertical line of elements, it should be understood that a columndoes not have to be arranged vertically (or longitudinally). Likewise, arow does not have to be arranged horizontally (or laterally). A row anda column may also sometimes describe an arrangement that is non-linear.Rows and columns also do not necessarily imply any parallel orperpendicular arrangement. Sometimes a row or a column may be referredto as a line. In other embodiments, there may be two or more lines ofLEDs for each color. In some embodiments, the number of lines of LEDsvary from color to color based on a brightness of each color. Forexample, red LEDs may be brighter than blue LEDs. To compensate for thedifference in brightness in an array, there may be 2 lines of red LEDsand 5 lines of blue LEDs on the array.

In one embodiment, the LEDs may be microLEDs. In other embodiments,other types of light emitters such as vertical-cavity surface-emittinglasers (VCSELs) may be used. A “microLED” may be a particular type ofLED having a small active light emitting area (e.g., less than 2,000 μm²in some embodiments, less than 20 μm² or less than 10 μm² in otherembodiments). In some embodiments, the emissive surface of the microLEDmay have a diameter of less than approximately 5 μm, although smaller(e.g., 2 μm) or larger diameters for the emissive surface may beutilized in other embodiments. The microLED may also have collimated ornon-Lambertian light output, in some examples, which may increase thebrightness level of light emitted from a small active light-emittingarea.

Example Formation of an Image

FIG. 5A is a diagram illustrating projection of light emitted from LEDsonto an image field, in accordance with an embodiment. FIG. 5Aillustrate how images are formed in a display device using light emittedfrom the light source 340. An image field is an area that receives thelight emitted by the light source 340 and forms an image. For example,an image field may correspond to a portion of the coupling element 350or a portion of the decoupling element 360 in FIG. 3A. In some cases, animage field is not an actual physical structure but is an area to whichthe image light is projected and which the image is formed. In oneembodiment, the image field is a surface of the coupling element 350 andthe image formed on the image field is magnified as light travelsthrough the output waveguide 320. In another embodiment, an image fieldis formed after light passing through the waveguide which combines thelight of different colors to form the image field. In some embodiments,the image field may be projected directly into the user's eyes.

During a scanning operation, a display device 500 uses a scanning mirror520 to project light from a light source 340 to an image field 530. Thedisplay device 500 may correspond to the near-eye display 100 or anotherscan-type display device. The light source 340 may correspond to thelight source 340 shown in FIG. 3B, or may be used in other displaydevices. The light source 340 includes an array 400 with multiple rowsand columns of light emitting devices, as represented by the dots ininset 515. In one embodiment, the light source 340 may include a singleline of light emitting diodes for each color. In other embodiments, thelight source 340 may include more than one line of LEDs for each color.The light 502 emitted by the light source 340 may be a set of collimatedbeams of light. For example, the light 502 in FIG. 5A shows multiplebeams that are emitted by rows of LEDs. Before reaching the mirror 520,the light 502 may be conditioned by different optical devices such as aconditioning assembly. The mirror 520 reflects and projects the light502 from the light source 340 to the image field 530. The mirror 520rotates about an axis 522. The mirror 520 may be amicroelectromechanical system (MEMS) mirror or any other suitablemirror. The mirror 520 may be an embodiment of the optics system 345 inFIG. 3B or a part of the optics system 345. As the mirror 520 rotates,the light 502 is directed to a different part of the image field 530, asillustrated by the reflected part of the light 504 in solid lines andthe reflected part of the light 504 in dash lines.

At a particular orientation of the mirror 520 (i.e., a particularrotational angle), the array 400 illuminate a portion of the image field530 (e.g., a particular subset of multiple pixel locations 532 on theimage field 530). In one embodiment, the LEDs are arranged and spacedsuch that a light beam from each LED is projected on a correspondingpixel location 532. The distance between adjacent rows of LEDs aredescribed with respect to FIGS. 6A and 6B. In another embodiment, smalllight emitters such as microLEDs are used for LEDs so that light beamsfrom a subset of multiple light emitters are together projected at thesame pixel location 532. In other words, a subset of multiple LEDscollectively illuminates a single pixel location 532 at a time.

The image field 530 may also be referred to as a scan field because,when the light 502 is projected to an area of the image field 530, thearea of the image field 530 is being illuminated by the light 502. Theimage field 530 may be spatially defined by a matrix of pixel locations532 (represented by the blocks in inset 534) in rows and columns. Apixel location here refers to a single pixel. The pixel locations 532(or simply the pixels) in the image field 530 sometimes may not actuallybe additional physical structure. Instead, the pixel locations 532 maybe spatial regions that divide the image field 530. Also, the sizes andlocations of the pixel locations 532 may depend on the projection of thelight 502 from the light source 340. For example, at a given angle ofrotation of the mirror 520, light beams emitted from the light source340 may fall on an area of the image field 530. As such, the sizes andlocations of pixel locations 532 of the image field 530 may be definedbased on the location of each light beam. In some cases, a pixellocation 532 may be subdivided spatially into subpixels (not shown). Forexample, a pixel location 532 may include a red subpixel, a greensubpixel, and a blue subpixel. The red subpixel corresponds to alocation at which one or more red light beams are projected, etc. Whensubpixels are present, the color of a pixel 532 is based on the temporaland/or spatial average of the subpixels.

The number of rows and columns of LEDs in the array 400 of the lightsource 340 may or may not be the same as the number of rows and columnsof the pixel locations 532 in the image field 530. In one embodiment,the number of LEDs in a row in the array 400 is equal to the number ofpixel locations 532 in a row of the image field 530 while the number ofLEDs in the array 400 in a column is two or more but fewer than thenumber of pixel locations 532 in a column of the image field 530. Putdifferently, in such embodiment, the light source 340 has the samenumber of columns of LEDs in the array 400 as the number of columns ofpixel locations 532 in the image field 530 but has fewer rows than theimage field 530. For example, in one specific embodiment, the lightsource 340 has about 1280 columns of LEDs in the array 400, which is thesame as the number of columns of pixel locations 532 of the image field530, but only 3 rows of LEDs. The light source 340 may have a firstlength L1, which is measured from the first row to the last row of LEDs.The image field 530 has a second length L2, which is measured from row 1to row p of the scan field 530. In one embodiment, L2 is greater than L1(e.g., L2 is 50 to 10,000 times greater than L1).

Since the number of rows of pixel locations 532 is larger than thenumber of rows of LEDs in the array 400 in some embodiments, the displaydevice 500 uses the mirror 520 to project the light 502 to differentrows of pixels at different times. As the mirror 520 rotates and thelight 502 scans through the image field 530 quickly, an image is formedon the image field 530. In some embodiments, the light source 340 alsohas a smaller number of columns than the image field 530. The mirror 520can rotate in two dimensions to fill the image field 530 with light(e.g., a raster-type scanning down rows then moving to new columns inthe image field 530).

The display device may operate in predefined display periods. A displayperiod may correspond to a duration of time in which an image is formed.For example, a display period may be associated with the frame rate(e.g., a reciprocal of the frame rate) representing the frequency thatan emission frame is repeated within a given time (e.g., 1 second). Inthe particular embodiment of display device 500 that includes a rotatingmirror, the display period may also be referred to as a scanning period.A complete cycle of rotation of the mirror 520 may be referred to as ascanning period. A scanning period herein refers to a predeterminedcycle time during which the entire image field 530 is completelyscanned. The scanning period may be divided into a plurality of emissionframes, each emission frame corresponding to light projected onto aparticular subset of pixel locations on the image field 530 (e.g., threerows of pixel locations on the image field). The scanning of the imagefield 530 is controlled by the mirror 520. The light generation of thedisplay device 500 may be synchronized with the rotation of the mirror520. For example, in one embodiment, the movement of the mirror 520 froman initial position that projects light to row 1 of the image field 530,to the last position that projects light to row p of the image field530, and then back to the initial position is equal to a scanningperiod. The scanning period may also be related to the frame rate of thedisplay device 500. By completing a scanning period, an image (e.g., aframe) is formed on the image field 530 per scanning period. Hence, theframe rate may correspond to the number of scanning periods in a second.

As the mirror 520 rotates, light scans through the image field andimages are formed. The actual color value and light intensity(brightness) of a given pixel location 532 may be an average of thecolor various light beams illuminating the pixel location during thescanning period. After completing a scanning period, the mirror 520reverts back to the initial position to project light onto the first fewrows of the image field 530 again, except that a new set of drivingsignals may be fed to the LEDs. The same process may be repeated as themirror 520 rotates in cycles. As such, different images are formed inthe scanning field 530 in different frames.

FIG. 5B is a diagram illustrating rows of pixel locations on an imagefield, in accordance with an embodiment. The image field 530 may includerows of pixel locations, each row including a plurality of pixellocations. In the example shown in FIG. 5B, there are z rows on theimage field 530. As the scanning mirror 520 rotates, light emitted fromthe array 400 is projected onto different portions of the image field530 to illuminate different rows of the image field 530 at a given time.

In one embodiment, all of the LEDs on the array 400 are driven to turnon at the beginning of an emission frame and emit light during anemission period that corresponds to a first half of the emission frame.During the emission period, light emitted from the array 400 isprojected onto the first three rows of pixel locations (e.g., Row 1, Row2, Row 3) on the image field 530. For example, red light emitted fromthe red LEDs 410 is projected onto Row 1, green light emitted from thegreen LEDs 420 is projected onto Row 2, and blue light emitted from theblue LEDs 430 is projected onto Row 3. After the emission frame, themirror 520 rotates such that in a subsequent emission frame, lightemitted from the array 400 is projected onto three rows of pixellocations on the image field 530 offset by one row compared to theprevious emission frame. For example, red light is now projected ontoRow 2, green light is projected onto Row 3, and blue light is projectedonto Row 4.

However, when all the LEDs on the array 400 are driven to emit light atthe same time during the emission period, there is a large instantaneouscurrent required to turn on all of the LEDs at the same time. But toprovide the current necessary to turn on all the LEDs of the array 400at the same time, the near-eye display 100 may be bulky because it needsa large current source and becomes expensive due to the high cost ofdesigning and manufacturing. Further, there is an increased risk ofsilicon not functioning properly over time due to being operated withhigh current as well as safety risk due to a large thermal budget thancannot be sunk easily. To reduce peak current, a time division methodmay be used to divide each emission frame into subframes and turn on adifferent portion of the LEDs on the array 400 in each of the subframesinstead of turning on all of the LEDs on the array 400 at the same time,as described below in detail with respect to FIGS. 6A and 6B.

FIG. 6A is a timing diagram illustrating emission patterns of LEDs whereeach emission frame has two subframes A, B, in accordance with anembodiment. A method of operating the array 400 is to turn on subsets ofLEDs on the array 400 at different subframes of an emission frame. Thecontroller 330 or the image processing unit 375 determines voltagevalues to apply to each of the LEDs 410 such that light emitted from theLEDs corresponds to a subpixel in a pixel location on the image field530. In the example shown in FIG. 6A, a first subset of LEDs on thearray 400 emits light during subframe A of the emission frame and asecond subset of LEDs on the array 400 emits light during subframe B ofthe emission frame that follows subframe A. In one embodiment, the firstsubset of LEDs are red LEDs 410 and the second subset of LEDs are greenLEDs 420 and blue LEDs 430. In another embodiment, the first subset ofLEDs and the second subset of LEDs may have different colors. Forexample, the first subset of LEDs may be green LEDs 420 and the secondsubset of LEDs may be red LEDs 410 and blue LEDs 430.

In the timing diagram shown in FIG. 6A, the red LEDs 410 that aredisposed on a first row of the array 400 emit light during subframe A ofeach emission frame. While the red LEDs 410 are turned on to emit light,the green LEDs 420 and the blue LEDs 430 are turned off. The green LEDs420 are disposed on a second row of the array 400 and emit light duringsubframe B that follows subframe A during each emission frame. The blueLEDs 430 are disposed on a third row of the array 400 below the greenLEDs 420 and emit light during subframe B at the same time as the greenLEDs 420. While the green LEDs 420 and the blue LEDs 430 are turned onto emit light, the red LEDs 410 are turned off.

To generate an image on the image field 530, light emitted from the redLEDs 410, green LEDs 420, and blue LEDs 430 are projected onto the imagefield 530. Each pixel on the image field 530 is divided into a redsubpixel, a green subpixel, and a blue subpixel. When all the LEDs onthe array 400 emit light at the same time, the rows of LEDs on the array400 are equal in between two adjacent rows.

However, when different portions of the LEDs are driven to emit light atdifferent times, the distance between the rows on the array 400 need tocompensate for the time delays to maintain image alignment on the imagefield 530. As shown in FIG. 4, the distance between red LEDs 410 and thegreen LEDs 420 is D1 and the distance between the green LEDs 420 and theblue LEDs 430 is D2, where the row of green LEDs 420 is between the rowof red LEDs 410 and the row of blue LEDs 430. When the array 400 isconfigured to turn on red LEDs during subframe A and turn on green LEDsduring subframe B, the distance D1 between the red LEDs 410 and thegreen LEDs 420 is equal to (n+½) times the distance D2 between the greenLEDs 420 and the blue LEDs 430, where n is 0 or an integer greater than0.

FIG. 6B is a timing diagram illustrating emission patterns of LEDs whereeach emission frame has three subframes A′, B′ C′, in accordance with anembodiment. During subframe A′, a first subset of LEDs emits light of afirst color. During subframe B′, a second subset of LEDs emits light,the second subset of LEDs of a second color different from the firstsubset of LEDs. During the subframe C′, a third subset of LEDs emitslight of a third color different from the first and the second colors.In the example shown in FIG. 6B, the first subset of LEDs is red LEDs410, the second subset of LEDs is green LEDs 420, and the third subsetof LEDs is blue LEDs 430. In other examples, the subset of LEDs may havedifferent colors from what is shown in FIG. 6B. The subframes A′, B′, C′may have equal time durations or have different time durations. However,the sum of the time durations for the subframes A′, B′, and C′ must beequal to or shorter than a time duration of a frame.

During subframe A′, the red LEDs 410 are turned on while the green LEDs420 and the blue LEDs 430 are turned off. During subframe B′, the greenLEDs 420 are turned on while red LEDs 410 and blue LEDs 430 are turnedoff. During subframe C′, the blue LEDs 430 are turned on while red LEDs410 and green LEDs 420 are turned off.

When there are three subframes and each row of LEDs on the array 400 isdriven to emit light during a different subframe as shown in the timingdiagram of FIG. 6B, the distance D1 between the red LEDs 410 and thegreen LEDs 420 and the distance D2 between the green LEDs 420 and theblue LEDs 430 are the same. However, the distances D1 and D2 are greaterthan the distance between adjacent rows for a display device that isconfigured to emit light from all three rows of the array 400 at thesame time during the emission frame (e.g., all three rows of the arrayemitting light during a first half of an emission frame).

FIGS. 7A-7C are conceptual diagrams illustrating rows onto which LEDsproject light for emission frames with two subframes as described abovewith reference to FIG. 6A, in accordance with an embodiment. During afirst subframe of each emission frame, a first subset of the LEDs on thearray 400 are turned on and a second subset of the LEDs on the array 400are turned off. During a second subframe of each emission frame thatfollows the first subframe, the first subset of the LEDs on the array400 are turned off and the second subset of the LEDs on the array 400are turned on. The red LEDs 410, the green LEDs 420, and the blue LEDs430 are operated by the controller 330 to turn on and off during theappropriate emission subframes to emit light. Light emitted from theLEDs are reflected off a surface of the mirror 520 that rotates to scanlight across the image field 530.

FIG. 7A illustrates projection of light onto the image field 530 duringa first emission frame. The number of LEDs in each row of the array 400matches the number of pixel locations in a row of the image field 530.As shown in the left diagram, red LEDs 410 on the array 400 are turnedon during a first subframe of a first emission frame of threeconsecutive emission frames. Light emitted from red LEDs 410 isprojected onto Row n of the image field 530 during the first subframe.Green LEDs 420 and blue LEDs 430 are turned off during the firstsubframe. Light emitted from each of the red LEDs 410 illuminates a redsubpixel of a pixel location on Row n of the image field 530.

As shown in the right diagram, red LEDs 410 are turned off during asecond subframe of the first emission frame, and the green LEDs 420 andblue LEDs 430 are turned on. Light emitted from the green LEDs 420 isprojected onto Row n−1 of the image field 530. Row n−1 is adjacent toRow n onto which the red LEDs 410 projected light during the firstsubframe. Light emitted from the blue LEDs 430 is projected onto Row n−2of the image field 530.

FIG. 7B illustrates projection of light onto the image field 530 duringa second emission frame after the first emission frame, according to oneembodiment. The mirror 520 redirects light emitted from the array 400such that light emitted from the red LEDs 410, green LEDs 420, and blueLEDs 430 are projected onto rows offset by one row compared to FIG. 7A.As shown in the left diagram, light from red LEDs 410 on the array 400are projected onto Row n+1 during a first subframe of a second emissionframe, where red LEDs 410 correspond to red subpixels of pixel locationson Row n+1. As shown in the right diagram, light from green LEDs 420 isprojected onto Row n and light from blue LEDs 430 is projected onto Rown−1. Light emitted from the green LEDs 420 corresponds to greensubpixels of pixel locations on the Row n, and light emitted from theblue LEDs 430 corresponds to blue subpixels of pixel locations on Rown−1.

FIG. 7C illustrates projection of light onto the image field 530 duringa third emission frame. As shown in the left diagram, light from redLEDs 410 is projected onto Row n+2 during a first subframe of the thirdemission frame. During a second subframe of the third emission frame,light from green LEDs 420 is projected onto Row n+1 and light from blueLEDs 430 is projected onto Row n.

Because each emission frame lasts for a short period of time (e.g., 345ns), when light emitted from one emission frame to the next isindistinguishable to the human eye. Over the three consecutive emissionframes shown in FIGS. 7A-7C, light emitted from red LEDs 410, green LEDs420, and blue LEDs 430 is projected onto Row n. The light emitted fromred LEDs 410 during the first subframe of the first emission frame, thelight emitted from green LEDs 420 during the second subframe of thesecond emission frame, and the light emitted from the blue LEDs 430during the second subframe of the third emission frame appear as one rowof pixels on Row n of the image field. Although light of differentcolors is projected at different times, each pixel appears as a singlecolor instead of three distinct subpixels that are each presented in adifferent emission frame because of the blurring and spatial integrationin the human eye of light.

Although not illustrated, in a fourth emission frame following the threeemission frame shown in FIGS. 7A-7C, light from red LEDs 410 isprojected onto Row n+3 during a first subframe, light from green LEDs420 is projected onto Row n+2 during a second subframe, and light fromblue LEDs 430 is projected onto Row n+1 during the second subframe. Thelight emitted from red LEDs 410 during the first subframe of the secondemission frame, light emitted from green LEDs 420 during the secondsubframe of the third emission frame, and light emitted from blue LEDs430 during the second subframe of the fourth emission frame appear asone row of pixels on Row n+1.

FIGS. 8A-8C are conceptual diagrams illustrating rows onto which LEDsproject light in emission frames with three subframes A′, B′ C′, inaccordance with an embodiment. FIG. 8A illustrates projection of lightonto the image field 530 during a first emission frame. The firstemission frame is divided into three subframes A′, B′, C′, and duringeach of the subframes, a different row of LEDs is turned on to emitlight. As shown in the left diagram, red LEDs 410 are turned on during afirst subframe of the first emission frame and projected onto Row nwhile the green LEDs 420 and blue LEDs 430 are turned off. As shown inthe middle diagram, the green LEDs 420 are turned on during a secondsubframe of the first emission frame and projected onto Row n−1 whilered LEDs 410 and blue LEDs 430 are turned off. As shown in the rightdiagram, the blue LEDs 430 are turned on during a third subframe of theemission frame and projected onto Row n−2 while red LEDs 410 and greenLEDs 420 are turned off.

FIG. 8B illustrates projection of light onto the image field 530 duringa second emission frame immediately after the first emission frame. Themirror 520 redirects light emitted from the array 400 such that lightemitted from the red LEDs 410, green LEDs 420, and blue LEDs 430 areprojected onto rows offset by one row compared to FIG. 7A. As shown inthe left diagram, red LEDs 410 are turned on during a first subframe ofthe second emission frame and projected onto Row n+1 while the greenLEDs 420 and blue LEDs 430 are turned off. As shown in the middlediagram, the green LEDs 420 are turned on during a second subframe ofthe second emission frame and projected onto Row n while red LEDs 410and blue LEDs 430 are turned off. As shown in the right diagram, theblue LEDs 430 are turned on during a third subframe of the secondemission frame and projected onto Row n−1 while the red LEDs 410 andgreen LEDs 420 are turned off.

FIG. 8C illustrates projection of light onto the image field 530 duringa third emission frame immediately after the second emission frame. Asshown in the left diagram, red LEDs 410 are turned on during a firstsubframe of the third emission frame and projected onto Row n+2 whilethe green LEDs 420 and blue LEDs 430 are turned off. As shown in themiddle diagram, the green LEDs 420 are turned on during a secondsubframe of the third emission frame and projected onto Row n+1 whilered LEDs 410 and blue LEDs 430 are turned off. As shown in the rightdiagram, the blue LEDs 430 are turned on during a third subframe of thethird emission frame and projected onto Row n while the red LEDs 410 andgreen LEDs 420 are turned off.

Light emitted from red LEDs 410 during the first subframe of the firstemission frame, light emitted from green LEDs 420 during the secondsubframe of the second subframe, and light emitted from blue LEDs 430during the third subframe of the third subframe appear as one row ofpixels on Row n of the image field.

Example Method of Operating Display Device

FIG. 9 is flowchart depicting a process of operating a display device,in accordance with an embodiment. The display device is configured tooperate 910 the first LEDs of a first color during first subframes ofemission frames to emit light from the first LEDs. The display device isconfigured to direct 920 the light emitted from the first LEDs onto aplurality of pixel locations of an image field. The light emitted fromthe first LEDs may be directed to a rotating mirror that projects thelight onto the plurality of pixel locations. The plurality of pixellocations may correspond to a row of pixels on the image field. Whilethe first LEDs emit light during the first subframes, the display deviceis configured to disable 930 second LEDs of a second color during thefirst subframes of the emission frames.

The display device is configured to operate 940 the second LEDs duringsecond subframes of the emission frames. The display device isconfigured to direct 950 the light emitted from the second LEDs onto theplurality of pixel locations of the image field. While the second LEDsemit light during the second subframes, the display device is configuredto disable 960 first LEDs during the second subframes of the emissionframes.

In some embodiments, the display device includes third LEDs of a thirdcolor. The display device may operate the third LEDs during the secondsubframes of the emission such that the second LEDs and the third LEDsemit light during the second subframes.

In other embodiments, the display device may operate the third LEDsduring third subframes of the emission frames. The display device may beconfigured to disable the first LEDs and the second LEDs during thethird subframes while the third LEDs emit light.

In some embodiments, the first LEDs are arranged along a first row of anarray, the second LEDs are arranged along a second row parallel to thefirst row at one side of the first row, and the third LEDs are arrangedalong a third row parallel to the first and second rows at an oppositeside of the first row.

The language used in the specification has been principally selected forreadability and instructional purposes, and it may not have beenselected to delineate or circumscribe the inventive subject matter. Itis therefore intended that the scope of the disclosure be limited not bythis detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

1. A display device comprising: a plurality of first light emittingdiodes (LEDs) configured to emit light of a first color onto a first rowof pixel locations on an image field during a first subframe of anemission frame but not during a second subframe of the emission frame,the first subframe not overlapping with the second subframe; a pluralityof second LEDs configured to emit light of a second color onto a secondrow of pixel locations different from the first row on the image fieldduring the second subframe of the emission frame but not during thefirst subframe of the emission frame; a mirror configured to reflect thelight emitted by the first LEDs onto the first row of pixel locationsduring the first subframe and reflect the light emitted by the secondLEDs onto the second row of pixel locations during the second subframe;and a controller configured to: operate the first LEDs and disable thesecond LEDs during the first subframe of the emission frame, and operatethe second LEDs and disable the first LEDs during the second subframe ofthe emission frame. 2-3. (canceled)
 4. The display device of claim 1further comprising: a plurality of third LEDs configured to emit lightof a third color onto a third row of pixel locations different from thefirst row and the second row of pixel locations, wherein the first LEDsare aligned along a first row, the second LEDs are aligned along asecond row parallel to the first row at one side of the first row, andthe third LEDs are aligned along a third row parallel to the first andsecond rows at an opposite side of the first row.
 5. The display deviceof claim 4, wherein the third LEDs are operated on by the controllerduring the first subframe of the emission frame and disabled by thecontroller during the second subframe of the emission frame.
 6. Thedisplay device of claim 5, wherein the first row is at a first distanceaway from the second row, and the first row is at a second distance awayfrom the third row, and wherein the first distance is (n+½) times thesecond distance, where n is 0 or an integer larger than
 0. 7. Thedisplay device of claim 4, wherein the third LEDs are operated by thecontroller during a third subframe of the emission frame and disabledduring the first subframe and the second subframe of the emission frame,the third subframe not overlapping with the first subframe or the secondsubframe.
 8. The display device of claim 7, wherein the first row is ata first distance away from the second row, and the first row is at asecond distance away from the third row, and wherein the first distanceis equal to the second distance.
 9. A method comprising: operating aplurality of first LEDs of a first color during a first subframe of anemission frame to emit light from the first LEDs; directing the lightemitted from the first LEDs onto a first row of pixel locations of animage field by reflecting the light emitted from the first LEDs off amirror during the first subframe of the emission frame; disabling aplurality of second LEDs of a second color during the first subframe ofthe emission frame; operating the second LEDs during the second subframeof the emission frame frame to emit light from the second LEDs;directing the light emitted from the second LEDs onto the second row ofpixel locations of the image field by reflecting the light emitted fromthe second LEDs off the mirror during the second subframe of theemission frame; and disabling the first LEDs during the second subframeof the emission frame, the first frame not overlapping with the secondsubframe. 10-11. (canceled)
 12. The method of claim 9, furthercomprising: operating a plurality of third LEDs to emit light from thethird LEDs, wherein the first LEDs are aligned along a first row, thesecond LEDs are aligned along a second row parallel to the first row atone side of the first row, and the third LEDs are aligned along a thirdrow parallel to the first and second rows at an opposite side of thefirst row.
 13. The method of claim 12, wherein the third LEDs areoperated during the first subframe of the emission frame and disabledduring the second subframe of the emission frame of the emission framesby a controller.
 14. The method of claim 13, wherein the first row is ata first distance away from the second row, and the first row is at asecond distance away from the third row, and wherein the first distanceis equal to (n+½) times the second distance where n is 0 or an integerlarger than
 0. 15. The method of claim 12, wherein the third LEDs areoperated during a third subframe of the emission frame and disabledduring the first subframe and the second subframe of the emission frame,the third subframe not overlapping with the first subframe or the secondsubframe.
 16. The method of claim 15, wherein the first row is at afirst distance away from the second row, and the first row is at asecond distance away from the third row, and wherein the first distanceis equal to the second distance.
 17. An array of LEDs comprising: aplurality of first LEDs arranged along a first row and configured toemit light of a first color onto a plurality of pixel locations on animage field; a plurality of second LEDs arranged along a second row atone side of the first row and separated from the first row by a firstdistance, the second LEDs configured to emit light of a second coloronto the plurality of pixel locations on the image field; and aplurality of third LEDs arranged along a third row at another side ofthe first row and separated from the first row by a second distance, thethird LEDs configured to emit light of a third color onto the pluralityof pixel locations on the image field, the first distance correspondingto (n+½) times the second distance where n is 0 or an integer largerthan
 0. 18. The array of LEDs of claim 17, wherein the second and thirdLEDs are configured to be operated at times when the first LEDs aredisabled during first subframes of emission frames.
 19. The array ofLEDs of claim 18, wherein the first LEDs are configured to be operatedat times when the second and third LEDs are disabled during secondsubframes of emission frames.
 20. The array of LEDs of claim 17, whereinlight emitted from the first, second, and third LEDs is reflected from amirror onto the plurality of pixel locations.